Which industrial Ethernet connector is better for use on the factory floor-the RJ-45 or the M-12?
By Raoul Benoit
The fast growth of Ethernet use on the factory floor is phenomenal. Two choices exist for Ethernet connectors in the industrial market: the RJ-45 and the M-12 (see Fig. 1). Is one better suited for harsh factory environments than the other? Can these two technologies coexist in the same marketplace?
When Ethernet first appeared on the market, it was designed for use in the office or home environment, which subject connectors to relatively tame amounts of electromagnetic interference (EMI), mechanical shock, noise, vibration, and temperature variation. The only splashdown going on is in the sink next to the office coffeepot. Ethernet using RJ-45 connectors fit well and could perform at optimal levels in the safe environs of the corporate office. However, the appeal and allure of real-time data acquisition by means of a relatively cheap, standardized product was too strong. Ethernet interconnects were hooked up to the factory floor, and the debate began in earnest.
Once the advantages of Ethernet in industrial applications were apparent, the next logical step was to adapt it to the environment it would be working in, and this meant protecting the RJ-45 from all the aforementioned hazards. Most of the adaptation involves protecting the RJ-45 connector by encasing it inside a molded housing. With this technology, some manufacturers have been able to achieve ingress-protection ratings of IP67 and IP68, the same degree of sealing that the M-12 connector can achieve. However, the initial concept and design of the M-12 was for harsh factory environments. To use an M-12 in an office environment would amount to overkill. From the design phase of development to the assembly of the M-12, every aspect of production has been geared to producing a product that will fit easily into the rugged conditions in the factory.
Receptacles
While the RJ-45 connector housing is made of plastic, the M-12 housing is made of metal. In terms of durability, toughness, and strength, a metal connector is vastly superior choice for performance on the factory floor. It makes sense that plant engineers would rather use rugged metal connectors made for the factory environment than use plastic connectors that have been adapted to work there.
The strength of the metal housing is only one reason the M-12 connector is so tough. The ruggedness of the M-12 starts with the design and assembly (see Fig. 2). Both the connectors and receptacles possess their own unique characteristics that provide them strength.
 FIGURE 2. For harsh-environment applications, the M-12 connector design incorporates heavy-duty insulation and shielding in a streamlined package. |
In the manufacturing of the M-12 receptacle, the outer jacket is stripped, and the inner jacket and the insulated conductors inside are wrapped with copper-foil shielding to protect the wiring from EMI. Then, terminal pin sleeves are slipped onto exposed conductors and inserted into an interior shell housing.
Next, by way of a keyway, the interior housing is fit into the exterior housing of the receptacle. Once this is completed, the whole assembly is filled with epoxy, completely encapsulating the conductors and terminals inside. The epoxy further strengthens the connector and protects it from temperature extremes, vibration, and moisture. Before the epoxy cures or hardens, a cylindrical metal tube is inserted into the housing, providing more shielding to the interior components. Once the metal tube is inserted, the epoxy takes about 24 hours to cure and adheres to the tube, providing a seal impenetrable to water, and further insulating the conductors from EMI.
After the epoxy and inserted metal tube have completely cured, the tubing is snugged to cable for extra strength by crimping it down tightly. After the crimping, further shielding is provided by a heat shrink tube that encompasses the whole metal tube.
The standard M-12 male connector has its own unique characteristics that protect it from the elements. It differs from the M-12 female receptacle because rather than employing the metal tubing to bond with epoxy filling, it uses overmolding that bonds directly to the cable’s outer jacket, providing a seal that effectively shuts out moisture and dust.
Outer molding
To enable a football linebacker to continue to play with a broken bone without further injury, medics use what can only be described as a huge padded club completely encasing the injury. Layer after layer of padding is wrapped around the broken bone. This approach is very similar to that employed by the RJ-45 Ethernet connector adapted to factory use.
Because the RJ-45 product is a widely used commodity, manufacturers save money on it because no labor dollars are spent on design and development. Use of the RJ-45 also saves money on tooling, because the machinery to produce it is already in place. Inventory is already on the shelf, ready to modify for adaptation to the factory floor. To adapt the RJ-45 to rugged industrial applications, layer upon layer of “padding” is added as an outer molding to prevent damage. This ruggedization approach is from the outside in, whereas the M-12 is ruggedized by design from inception, or from the inside out. Because of this, the M-12 has a much leaner appearance, and is a better choice where real estate is limited (see Fig. 3).
 FIGURE 3. Overmolded M-12 connectors in a Profinet implementation of an industrial Ethernet system plug into a machine-mounted Ethernet switch. |
Can the two types of technology exist side by side? Yes. If a system integrator wanted to use the RJ-45 inside the relative safety of a PLC cabinet, it could have an M-12 connector used as the pass-through connector, which would be strong enough to face the environmental challenges outside of the enclosure. With the development of innovative products like interface adapters, both technologies could be incorporated into one Ethernet network (see Fig. 4).
 FIGURE 4. Both the RJ-45 and M-12 connector can be incorporated into the same industrial Ethernet application. |
While the RJ-45 offers some attractive options like lower upfront costs to integrate and the same level of ingress protection as the M-12, the numbers eventually illuminate one conclusion. The M-12 is inherently stronger, more streamlined, and will last longer. Ultimately, durability is the predominant factor for decision makers considering long-term costs. The marketplace, as always, will make final choice.
ACKNOWLEGEMENT
The author would like to thank Karsten Loehken and Bernie Baruffalo of Lumberg for help on the article.
RAOUL BENOIT is marketing communications coordinator for Lumberg, 14121 Justice Road, Midlothian, VA 23113. Tel: (804) 379-2010; Email: rbenoit@lumbergusa.com.
